People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

For the first study linking the mutations to schizophrenia, scientists analyzed the genes of more than 12,300 people, almost 5,000 of whom had schizophrenia. They found that protein-damaging variations expressed in the brain “were more abundant among individuals with schizophrenia than among controls,” the study says, at a high rate that suggests inheritance of those genes. The part of the brain affected most was the neurons, and the researchers suggested that dysfunction in the synapses — the pathways between neurons through which information is passed — heavily influences the risk of developing schizophrenia.

Certain genetic mutations in the brain could reveal a lot about a person's propensity to leave school early or develop a mental disorder.Pixabay public domain

In the second study, scientists compared a similar kind of group of rare genetic mutations to the amount of time subjects stayed in school, to indirectly measure the effect of these mutations on general cognitive abilities. The tallies varied, with one mutation being linked to three fewer months of schooling than the average student and another to six months fewer. Based on consistent results in people both with and without severe neurodevelopmental disorders, such as schizophrenia, autism, mental retardation and bipolar disorder, the researchers suggested that protein-damaging genetic mutations in the brain “influence the cognitive spectrum in the general population,” rather than just those with the severe disorders.

But this is not the end of the research. According to the first study, “Because of the rareness of these variants and the infrequency with which any individual gene is affected by them, even among schizophrenia cases, the sequencing of much larger cohorts will be needed to identify the specific individual genes in which rare variants shape risk for schizophrenia.”